(1) Magnet Damping Mechanism
With reference to FIG. 10, a magnet damping mechanism 700 of the prior art has a conductive working member 730 movably arranged between a pair of magnets 720 and 721 of which magnetic poles are so arranged that an attractive force is caused therebetween. A damping force is caused in the working member 730 by electromagnetic induction due to axial movement of the working member 730. In addition, an attractive force is caused between the magnets 720 and 721 and a ferromagnetic member 732 arranged within the working member 730. Thus, the magnet damping mechanism 700 exhibits a self-aligning function to stably hold the working member 730 at a predetermined position (see e.g Document 1: Japanese Laid-open Patent Publication No. 21923/2002).
(2) a Mechanism for Holding a Stable Condition at Two Positions Using Magnets
With reference to FIG. 11, a mechanism 800 for holding a stable condition at two positions using magnets of the prior art comprises a camera cone 802 and a roll ring 804. A camera cone thread 806 is formed on the outer circumferential surface of the camera cone 802 and a roll ring thread 808 is formed on the inner circumferential surface of the roll ring 804. The roll ring thread 808 is screwed on the camera cone thread 806 and is snugly engaged therewith. The camera cone thread 806 and the roll ring thread 808 may be ordinary threads, grease threads or the combination thereof. A main magnet 810 is arranged on the roll ring 804 along its inner circumferential surface. A follower magnet 812 is rotatably arranged at a position inside the inner circumferential surface of the roll ring 804. An indicating member 820 is secured on the follower magnet 812. A first stopper 822 is secured on the camera cone 802 for limiting the rotation of the indicating member 820 in its clockwise direction. A second stopper 824 is also secured on the camera cone 802 for limiting the rotation of the indicating member 820 in its anticlockwise direction. A tip 820t of the indicating member 820 is positioned at the center of the camera cone 802 in a condition when the indicating member 820 contacts the second stopper 824 (shown by a dotted line in FIG. 11). The tip 820t of the indicating member 820 is positioned at a position out of a window 802b of the camera cone 802 in a condition when the indicating member 820 contacts the first stopper 822.
In a condition in which the indicating member 820 contacts the first stopper, the N pole of the main magnet 810 repulses the N pole of the follower magnet 812 and thus rotates the follower magnet 812 in a clockwise direction. Under the condition in which the indicating member 820 contacts the first stopper, if the roll ring 804 is rotated in a clockwise direction, the S pole of the main magnet 810 attracts the N pole of the follower magnet 812 and thus rotates the indicating member 820 in an anticlockwise direction. If the roll ring 804 is further rotated in a clockwise direction until the S pole of the main magnet 810 is positioned nearest to the N pole of the follower magnet 812, the indicating member 820 will occupy the position in which it contacts the second stopper 824 (shown by the dotted line in FIG. 11).
(3) a Mechanism for Holding a Stable Condition at Two Positions Using a Reversible Self-Holding Elastic Member
With reference to FIG. 12, the mechanism 900 for holding a stable condition at two positions using a reversible self-holding elastic member of the prior art has a working lever 904 pivotably mounted on a working lever pin 910 secured on a base member 902. A positioning pin 908 is mounted on the working lever 904 for securing one end 906a of a reversible self-holding elastic member 906. The end 906a of the reversible self-holding elastic member 906 is secured on the positioning pin 908 by winding it around the pin 908. The other end 906b of the reversible self-holding elastic member 906 is secured on a mount pin 916 secured on the base member 902 by winding it around the mount pin 916. A working member 920 is assembled to two guiding portion 910c and 910d on the base member 902 so that it can slide therein. A driving pin 922 mounted on the working member 920 is arranged within an elongated hole 904h formed in the driving pin 922.
Initially the working lever 904 is positioned at a position shown by a solid line in FIG. 12 by the elastic force of the reversible self-holding elastic member 906. Then the working lever 904 is positioned at a position shown by a dotted line in FIG. 12 by manually rotating the working lever 904 in an anticlockwise direction. If then manually rotating the working lever 904 in a clockwise direction, the working lever 904 will be returned to and positioned again at the position shown by a solid line in FIG. 12. During the rotation of the working lever 904, the working member 902 can be slid within the guiding portions 910c and 910d due to the movement of the elongated hole 904h and thus the driving pin 922. The slidable stroke of the working member 920 is shown as “DS” in FIG. 12. The working lever 904 may be driven by a suitable means such as a solenoid.
Said Document 1 is Japanese Laid-open Patent Publication No. 21923/2002 (Pages 3˜5, FIGS. 1˜3).
(4) Problem of the Magnet Damping Mechanism
This mechanism can achieve the self-aligning function with the generation of the damping force. However, it is impossible to stop the working member at two predetermined positions.
(5) Problem of the Mechanism for Holding a Stable Condition at Two Positions Using Magnets
This mechanism requires, in order to rotate the follower magnet, to rotate the main magnet until the rotational driving force is generated in the follower magnet. According to this mechanism, the indicating member is rotated in an anticlockwise direction by rotating the roll ring in a clockwise direction so that the S pole of the main magnet attracts the N pole of the follower magnet. Accordingly, since the gradient of the change in actuating force from the main magnet relative to the rotational angle of the follower magnet becomes gentle, it is impossible to reduce the hysteresis of the actuating force applied to the follower magnet by the main magnet.
(6) Problem of the Mechanism for Holding a Stable Condition at Two Positions Using a Reversible Self-Holding Elastic Member
According to this mechanism of the prior art, it is difficult to stabilize the operation of the reversible self-holding elastic member because of the reduction of the elastic force of the reversible self-holding elastic member when the stroke for moving the working lever to the reversed position is reduced. Accordingly, it is required to sufficiently increase the distance between the center of rotation of the working lever and the positioning pin. However, in order to set the movable stroke of the working member at about 0.1 mm, it is afraid that that the distance between the center of rotation of the working lever and the positioning pin would become large beyond the practical length adaptable to ordinary cameras or cellular-phones.